warming we are feeling now is mostly from GHG emissions from decades ago. GHGs are like a lid on a pot; as the lid gets thicker the stuff in the pot gets warmer, but it takes some time...in this case probably 20-30 years. The warming we have seen so far is primarily from emissions up to 1990, so about 350 ppm.
Actually, no, that's not true; http://iopscience.iop.org/article/10.1088/1748-9326/9/12/124002;jsessionid=BC6F9B408139804AB3587C183EE22AAC.c1.iopscience.cld.iop.org
Maximum warming occurs a median of 10.1 years after the CO2 emission event and has a median value of 2.2 mK GtC−1.
We now can reasonably deny the validity to apply this research paper to polar amplification without a shade of doubt:
Palaeoclimate constraints on the impact of 2° C anthropogenic warming and beyond (P. Bakker et al ), Nature Geoscience June 2018
free version:
http://eprints.esc.cam.ac.uk/4301/2/41561_2018_146_MOESM1_ESM.pdfThe paper is very well articulated and documented, probably the most updated paper on past reconstruction of warming events due to orbital forcing and GHG, the main purpose of the paper is to back test the validity of the models -used for our current man made GW- to these paleoclimatic events.
on page 4 of the article, we can read the following:
"The MPWP (mid-Pliocene warm period 3.3–3.0 million years ago)
was subject to intermittently elevated CO2 (potentially up to 450 ppm)
compared to the HTM (Holocene Thermal Maximum) and the LIG9 (last Interglacial).
The CO2 concentration at that time was most similar to the RCP2.6
scenario, and a factor of three-to-four less than concentrations
expected by ad 2100 for the RCP8.5 scenario. Climate models
simulate an increase in tropical temperatures by 1.0–3.1 °C (for
RCP2.6 CO2 forcing of 405 ppmv (ref. 2)), generally in line with
MPWP proxy reconstructions at low latitudes127. Strong polar
amplification is observed for the MPWP. For example, proxy data
from the North Atlantic and northeastern Russian Arctic indicate a
rise of surface air temperatures by 8 °C (ref. 128) during the MPWP
and even higher in the early Pliocene129. These regional temperature
changes are similar to projected warming at ad 2100 for the RCP8.5
scenario, in spite of the much lower CO2 rise during the MPWP,
and suggest that current models may underestimate the warming
response in the Arctic130 to increased CO2 concentrations."